Biomedical subjects

A Menand

Publications and source records attributed to A Menand.

5 recordsLinked to original sources

PubMed2002

Field evaporation behaviour in the gamma phase in Ti-Al during analysis in the tomographic atom probe.

A Ti-48 at% Al alloy has been successfully investigated, using atom probe field ion microscopy and transmission electron microscopy. After a specific heat treatment, this alloy has a (alpha2 + gamma) lamellar microstructure. Using the tomographic atom probe (TAP), it has been possible to image the stacking of superlattice planes of gamma and to identify titanium as the highest evaporation field element. In addition, the influence of analysis site on atom probe measurements has been estimated for this phase. A TAP analysis has also made it possible to observe an extremely thin step along a gamma/gamma interface at a near atomic scale.

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PubMed2001

A model accounting for spatial overlaps in 3D atom-probe microscopy.

The spatial resolution of three-dimensional atom probe is known to be mainly controlled by the aberrations of ion trajectories near the specimen surface. An analytical model accounting for the spatial overlaps that occur near phase interfaces is described. This model makes it possible to correct the apparent composition of small spherical precipitates in order to determine the true composition. The prediction of the overlap rate as a function of the particle size was found in remarkably good agreement with the simulations of ion trajectories that were made. The thickness of the mixed zone around beta precipitates was found to be of 0.3 nm for a normalised evaporation field of beta phase of 0.8. Using simulations, the overlap rate could be parameterised as a function of the apparent atomic density observed in particles. This model has been applied to copper precipitation in FeCu.

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PubMed2001

Structural analyses in three-dimensional atom probe: a Fourier transform approach.

The three-dimensional atom probe (3DAP) technique gives the elemental identities and the position of atoms within the small volume analysed (on the order of 10 x 10 x 100 nm(3)). The large number of atoms collected (up to two million) and the excellent spatial resolution of this instrument allows the observation of some crystallographic features of phases chemically identified. This paper shows that the application of a discrete Fourier transform algorithm to a 3DAP dataset provides information that is not easily accessible in real space. The derivation of the mean size of particles from Fourier intensities is an example. Using 3D 'dark-field' imaging, single ordered grains were isolated from the disordered matrix of a ternary alloy. Moreover, the intrinsic spatial resolution of the instrument was evaluated by this method for pure metal; the resolution reaches 0.2 nm laterally and 0.06 nm in depth. This excellent resolution is shown to be sufficient to give access to the crystalline lattice. The use of image filtering in the reciprocal space enables for atomic columns to be imaged the first time from 3DAP data.

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PubMed1999

Three-dimensional atomic-scale imaging of impurity segregation to line defects

Clouds of impurity atoms near line defects are believed to affect the plastic deformation of alloys. Three-dimensional atom probe techniques were used to image these so-called Cottrell atmospheres directly. Ordered iron-aluminum alloys (40 atomic percent aluminum) doped with boron (400 atomic parts per million) were investigated on an atomic scale along the <001> direction. A boron enrichment was observed in the vicinity of an <001> edge dislocation. The enriched region appeared as a three-dimensional pipe 5 nanometers in diameter, tangent to the dislocation line. The dislocation was found to be boron-enriched by a factor of 50 (2 atomic percent) relative to the bulk. The local boron enrichment is accompanied by a strong aluminum depletion of 20 atomic percent.

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PubMed1999

Tomographic Atom Probe: New Dimension in Materials Analysis.

: Materials science requires the use of increasingly powerful tools in materials analysis. The last 20 years have witnessed the development of a number of analytical techniques. However, among these techniques, only a few allow observation and analysis of materials at the nanometer level. The tomographic atom probe (TAP) is a three-dimensional atom-probe (3-DAP) developed at the University of Rouen. In this instrument, the specimen is field evaporated, atomic layer by atomic layer, and the use of a position-sensing system makes it possible to map out the chemical identity of individual atoms within each field-evaporated layer on a nearly atomic scale. After analysis, the volume of matter removed from the specimen can be reconstructed atom by atom in the three dimensions of real space. The main advantages of the 3-DAP is its single-atom sensitivity and very high spatial resolution. In addition to 3-D visual information on chemical heterogeneity, 3-D images give an accurate measurement of the composition of any feature without any convolution bias. This study first describes the history of the 3-DAP technique. Its main features and the latest developments of the TAP are then detailed. The performance of this instrument is illustrated through two recent applications in materials science. Possible ways to further improve the technique are also discussed.

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